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Sound transmission through double doors
Quirt, J. D.
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Ser
N21d
*
National Research
Council Canada
Conseil national
de recherches Canada
,
no. 14221
c. 2Institute for
lnstitut de
B r n .
- . .. ~- - 1
Research in
recherche en
Construction
construction
Sound Transmission
Through Double Doors
Reprinted from
Canadian Acoustics
Vol. 14, No. 4, 1986
p. 3-10
(IRC Paper No. 1422)
Price $2.00
NRCC 2671 1
L NRC-
CISTII R C
L I B R A R Y
fEB 5
1!67
1B I B L I O T H ~ Q U E
1
I R C
CNRC-
IC19T1
Ser National Research Council
TH1
Canada. I n s t i t u t e f o r N21d Research i n Construction no. 1422
Paper c. 2
SOUND TRANSMISSION THROUGH DOUBLE DOORS J.D. Q u i r t , A c o u s t i c s S e c t i o n , I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n , N a t i o n a l R e s e a r c h C o u n c i l of Canada, Ottawa, O n t a r i o , K 1 A OR6. ABSTRACT
T h i s r e p o r t p r e s e n t s t h e r e s u l t s of a series of tests t o e v a l u a t e sound t r a n s m i s s i o n t h r o u g h a d o u b l e d o o r system (two d o o r s w i t h a n a i r s p a c e between). The main p u r p o s e of t h e s e t e s t s w a s t o e s t a b l i s h t h a t such a system u s i n g c o n v e n t i o n a l door p a n e l s can p r o v i d e s u b s t a n t i a l n o i s e r e d u c t i o n . The secondary g o a l of t h e series was t o e v a l u a t e t y p i c a l o f f i c e d o o r s i n c l u d i n g t h e e f f e c t of minor m o d i f i c a t i o n s t h a t c o u l d i n c r e s e t h e n o i s e r e d u c t i o n p r o v i d e d by t h e door system.
SOMMAIRE
C e r a p p o r t p r g s e n t e les r g s u l t a t s d'une s g r i e d ' e s s a i s v i s a n t
A
& v a l u e r l at r a n s m i s s i o n du s o n
A
t r a v e r s un syst&me d e p o r t e d o u b l e (deux p o r t e s s & p a r & e s p a r une lame d ' a i r ) . Le p r i n c i p a l o b j e c t i f v i s g & t a i t d e montrer qu'un p a r e i l syst&me, c o n s t i t u k d e panneaux de p o r t e c l a s s i q u e s , p e u t a s s u r e r une r 6 d u c t i o n i m p o r t a n t e du b r u i t . L ' o b j e c t i f s e c o n d a i r e c o n s i s t a i tA
& v a l u e r l a performance d e s p o r t e s d e bureau t y p e s , notamment l ' e f f e t de m o d i f i c a t i o n s mineures s u s c e p t i b l e s d e r h d u i r e d a v a n t a g e l a t r a n s m i s s i o n du b r u i tA
t r a v e r s l e s s y s t h e s d e p o r t e s .INTRODUCTION
The main p u r p o s e of t h e s e t e s t s was t o e s t a b l i s h t h a t a d o u b l e d o o r system
(comprising two c o n v e n t i o n a l d o o r s w i t h a n a i r s p a c e between) c a n p r o v i d e s u f f i c i e n t n o i s e r e d u c t i o n f o r c o n f i d e n t i a l s p e e c h p r i v a c y
-
i n s p e c i f i c , t h a t t h e y can a c h i e v e a sound t r a n s m i s s i o n c l a s s (STC) of 4 5 o r h i g h e r . An STC of a b o u t 4 5 i s r e q u i r e d t op r o v i d e c o n f i d e n t i a l s p e e c h p r i v a c y i n a t y p i c a l o f f i c e environment. The secondary g o a l of t h e s e r i e s was t o e v a l u a t e t y p i c a l d o o r s i n c l u d i n g t h e performance of
w e a t h e r s t r i p p i n g and o t h e r f e a t u r e s t h a t c o u l d a f f e c t t h e n o i s e r e d u c t i o n p r o v i d e d by t h e door system i n t h e l o n g o r s h o r t t e r m .
Because of t h e l a r g e p o t e n t i a l b e n e f i t s ( s a v i n g s f o r major l a n d l o r d s , o r improved " o f f i c e performance f o r o c c u p a n t s ) i f a n i n e x p e n s i v e a l t e r n a t i v e t o commercial
a c o u s t i c a l d o o r s c a n b e d e v e l o p e d , an e x t e n s i v e series of tests was performed. I n t o t a l , t h i r t y t h r e e sound t r a n s m i s s i o n t e s t s were r u n , i n c l u d i n g f i v e c a s e s t h a t were r e p e a t e d t o t e s t v a r i a b i l i t y of t h e a c o u s t i c a l performance of w e a t h e r s t r i p p i n g . Two t y p e s of w e a t h e r s t r i p p i n g were t e s t e d , and t o a s s e s s t h e i r e f f e c t i v e n e s s ,
measurements were a l s o made w i t h t h e d o o r s s e a l e d . The tests used two t y p e s of d o o r s ( a s o l i d - c o r e wood door and a h o l l o w m e t a l d o o r ) t o d e t e r m i n e whether t h e i r a c o u s t i c a l d i f f e r e n c e s would b e s i g n i f i c a n t i n t h i s a p p l i c a t i o n . Two door frame systems were t e s t e d , t o show t h e dependence of t h e sound t r a n s m i s s i o n on t h e s p a c e between t h e two d o o r s , and t o e s t a b l i s h t h e minimum i n t e r - d o o r s p a c i n g t h a t c o u l d r e l i a b l y a c h i e v e t h e t a r g e t of STC 4 5 . The e f f e c t of a d d i n g a c o u s t i c a l l y a b s o r b i n g
DESCRIPTION OF THE MEASUREMENTS
The sound t r a n s m i s s i o n c h a r a c t e r i s t i c s of t h e doors were determined i n accordance w i t h ASTM S t a n d a r d E90-85, "Standard Method f o r L a b o r a t o r y Measurement of Airborne Sound T r a n s m i s s i o n Loss of B u i l d i n g Elements". The Sound T r a n s m i s s i o n C l a s s (STC) was c a l c u l a t e d from t h e r e s u l t i n g sound t r a n s m i s s i o n l o s s d a t a , i n a c c o r d a n c e w i t h ASTM S t a n d a r d C l a s s i f i c a t i o n E413-73.
The t r a n s m i s s i o n l o s s e x p r e s s e s i n d e c i b e l s what f r a c t i o n of t h e sound e n e r g y
s t r i k i n g a b u i l d i n g element i s t r a n s m i t t e d through i t . The h i g h e r t h e t r a n s m i s s i o n l o s s , t h e b e t t e r t h e n o i s e r e d u c t i o n by t h e element. The ASTM E90 t e s t method r e q u i r e s measurement of t r a n s m i s s i o n l o s s i n t h e 16 s t a n d a r d 113-octave frequency bands whose c e n t r e f r e q u e n c i e s r a n g e from 125 Hz t o 4000 Hz; normal p r a c t i c e i n t h i s l a b o r a t o r y i n c l u d e s measurements i n a d d i t i o n a l frequency bands. Although t h e d a t a f o r a l l of t h e s e f r e q u e n c y bands a r e u s e f u l f o r a n a l y s i s of t h e f a c t o r s c o n t r o l l i n g sound t r a n s m i s s i o n , a s i n g l e - f i g u r e r a t i n g i s r e q u i r e d f o r c o n v e n i e n t comparison of two o r more e l e m e n t s .
I n k e e p i n g w i t h common p r a c t i c e , t h e r a t i n g used h e r e i s t h e Sound T r a n s m i s s i o n C l a s s (STC). T h i s r a t i n g h a s been shown t o c o r r e l a t e w e l l w i t h s u b j e c t i v e i m p r e s s i o n s of t h e sound i n s u l a t i o n p r o v i d e d a g a i n s t sounds such a s speech.
The door frame was i n s t a l l e d i n a p a r t i t i o n 2.44 m h i g h x 3.05 m wide i n t h e t e s t frame between two r e v e r b e r a t i o n rooms. T h i s p a r t i t i o n was s u p p o r t e d by two rows of l i g h t w e i g h t 9 0 mm s t e e l s t u d s ; a 25 mm s p a c e s e p a r a t e d t h e two rows of s t u d s . G l a s s f i b r e b a t t s of nominal 90 mm t h i c k n e s s were p l a c e d between t h e s t u d s i n each row. Two l a y e r s o f 16 mm gypsum w a l l b o a r d we e a p p l i e d t o each f a c e of t h i s p a r t i t i o n ;
5
t h e nominal s u r f a c e d e n s i t y was 23 kglm.
The w a l l d e t a i l s and frame i n s t a l l a t i o n a r e shown i n F i g s . 1 and 2.T e s t s w i t h t h e door opening blocked showed t h a t t h e p a r t i t i o n had h i g h e r
t r a n s m i s s i o n l o s s t h a n t h e doors a t a l l f r e q u e n c i e s ( t h e w a l l STC w a s 6 1 ) . I n t h e f o l l o w i n g a n a l y s i s of t h e t e s t r e s u l t s , sound t r a n s m i s s i o n through t h e p a r t t i o n may
9
b e i g n o r e d i n most c a s e s , and t h e d o u b l e door system (whose a r e a was 2.23 m ) i s t r e a t e d a s t h e o n l y sound t r a n s m i s s i o n path. I n t h e c a s e of t h e b e s t door systems, f l a n k i n g t r a n s m i s s i o n through t h e s u r r o u n d i n g p a r t i t i o n s l i g h t l y reduced t h ea p p a r e n t t r a n s m i s s i o n l o s s a t low f r e q u e n c i e s . The t r u e t r a n s m i s s i o n l o s s e s of t h e d o o r systems were c a l c u l a t e d ( u s i n g t h e measured t r a n s m i s s i o n l o s s of t h e gypsum b o a r d p a r t i t i o n ) and t h e c o r r e c t e d d a t a a r e p r e s e n t e d below. Even f o r t h e b e s t d o o r s , t h i s s y s t e m a t i c d i s t o r t i o n of t h e r e s u l t s d i d n o t r e d u c e t h e STC by more t h a n 2 dB, and f o r d o o r s whose STC was under 4 5 , t h e e f f e c t of f l a n k i n g was less t h a n t h e measurement u n c e r t a i n t y . O v e r a l l , t h e e f f e c t of f l a n k i n g was l e s s s e r i o u s t h a n t h e v a r i a b i l i t y a s s o c i a t e d w i t h how f i r m l y t h e door was l a t c h e d , and how t h e
w e a t h e r s t r i p p i n g mated w i t h t h e door s u r f a c e s . DESCRIPTION OF DOOR SYSTEMS
The wood door was a s t a n d a r d commercial s o l i d - c o r e door w i t h h a r d b o a r d f a c e s . The door dimensions were 2134 mm h i g h x 914 mm wide x 45 mm t h i c k . Weight of t h e door w a s 46.7 kg w i t h hardware. The s t e e l door was a commercial h o l l o w m e t a l door w i t h
18 gauge wipecoat g a l v a n i s e d s t e e l f a c e s and 20 gauge i n t e r n a l s t e e l s t i f f e n e r s . The door dimensions were 2115 mm h i g h x 905 mm wide x 45 mm t h i c k . Weight of t h e d o o r was 50.1 kg w i t h hardware.
For t h e f i r s t s e r i e s of t e s t s , t h e two d o o r s were mounted on o p p o s i t e s i d e s of a
s i n g l e door frame o f 16-gauge p r e s s e d s t e e l w i t h a n opening 2135 mm h i g h x 915 mm
wide. To r e d u c e sound t r a n s m i s s i o n due t o v i b r a t i o n of t h e door frame i t s e l f , two
I l a y e r s of 16 mm gypsum w a l l b o a r d were f a s t e n e d i n s i d e t h i s frame a s shown i n F i g . 1, i
and a l l v i s i b l e c r a c k s and h o l e s were plugged w i t h c a u l k i n g . The s p a c e between t h e s u r f a c e s of t h e two d o o r s was 65 mm. To o b t a i n a l a r g e r s p a c i n g between t h e d o o r s , f o r t h e second s e r i e s of tests t h e d o o r s were mounted i n a d j o i n i n g 16-gauge p r e s s e d - s t e e l door frames w i t h door s e p a r a t i o n of 228 mm, a s shown i n F i g u r e 2.
Fig. 1: Cross s e c t i o n s k e t c h showing Fig. 2: Cross s e c t i o n s k e t c h showing i n s t a l l a t i o n of t h e s i n g l e doorframe i n s t a l l a t i o n of t h e double doorframe i n t h e p a r t i t i o n . Door s e p a r a t i o n i n t h e p a r t i t i o n . Door s e p a r a t i o n i s
i s 65 mm. 228 mm.
Components a r e : ( 1 ) g l a s s f i b r e b a t t s between s t u d s and i n s i d e doorframe, (2) d o u b l e l a y e r of 16 mm t h i c k gypsumboard, ( 3 ) 16 mm t h i c k plywood,
( 4 )
c l o s e d - c e l l foam w e a t h e r s t r i p compressed between door and frame, (5) h o l l o w m e t a l door, ( 6 ) s o l i d c o r e wood d o o r , ( 7 ) 16 gauge p r e s s e d s t e e l doorframe, ( 8 ) 25 mm t h i c k open c e l l p o l y u r e t h a n e a c o u s t i c a l foam, (9) m a g n e t i c w e a t h e r s t r i p .Conventional h i n g e s , door h a n d l e s , l a t c h e s , and s t r i k e p l a t e s were i n s t a l l e d t o p e r m i t normal opening and c l o s i n g of b o t h doors. A t t h e bottom of t h e door, a plywood t h r e s h o l d gave e s s e n t i a l l y t h e same p r o f i l e a s t h e door frame had a t t h e s i d e s of t h e door.
For some of t h e tests w i t h each door frame system, w e a t h e r s t r i p w a s i n s t a l l e d t o r e d u c e sound t r a n s m i s s i o n around t h e f o u r edges of each door. With t h e s i n g l e frame
(65 mm between t h e d o o r s ) two t y p e s of w e a t h e r s t r i p were t e s t e d : c l o s e d c e l l foam and a magnetic t y p e s i m i l a r t o r e f r i g e r a t o r door g a s k e t s . Only t h e magnetic
w e a t h e r s t r i p was t e s t e d w i t h t h e l a r g e r (228 mm) s p a c e between t h e doors. T y p i c a l l o c a t i o n of t h e foam o r magnetic w e a t h e r s t r i p a r e shown i n t h e expanded d e t a i l s i n F i g u r e s 1 and 2. S e l f - a d h e s i v e m e t a l s t r i p s ( t o mate w i t h t h e magnetic
w e a t h e r s t r i p ) were a p p l i e d t o t h e f a c e of t h e wood door. With each s p a c i n g between t h e d o o r s , a c o u s t i c a l l y a b s o r b i n g m a t e r i a l was mounted on t h e f a c e of one o r b o t h of
t h e d o o r s f o r some of t h e t e s t s . The l o c a t i o n of t h e a b s o r b i n g m a t e r i a l i s
i l l u s t r a t e d i n F i g u r e 1 . The m a t e r i a l used was 2 5 mm t h i c k open c e l l p o l y u r e t h a n e a c o u s t i c a l foam; i n some c a s e s w i t h t h e l a r g e r s p a c e between t h e d o o r s , a double l a y e r was used.
MAJOR
TEST RESULTSI t was c l e a r l y e s t a b l i s h e d t h a t a s i m p l e d o u b l e door system, u s i n g two c o n v e n t i o n a l d o o r s w i t h t y p i c a l gaps a t t h e p e r i m e t e r and no s p e c i a l a c o u s t i c a l t r e a t m e n t , w i l l n o t g i v e a n STC a s h i g h a s 4 5 . With q u i t e s i m p l e m o d i f i c a t i o n s , however, a n STC a p p r e c i a b l y above STC 4 5 i s a t t a i n a b l e . A summary of t h e t e s t r e s u l t s i s p r e s e n t e d i n t h e f o l l o w i n g t a b l e . T h i s is followed by a b r i e f d i s c u s s i o n of t h e a c o u s t i c a l e f f e c t of v a r i o u s m o d i f i c a t i o n s t o t h e door system.
T a b l e 1 : T y p i c a l Sound T r a n s m i s s i o n C l a s s (STC) v a l u e s f o r door systems t e s t e d .
To examine t h e s i g n i f i c a n c e of l e a k a g e around t h e doors and compare t h e a c o u s t i c a l p o t e n t i a l of t h e two t y p e s of d o o r s , e a c h door was t e s t e d by i t s e l f w i t h s e v e r a l
t r e a t m e n t s t o r e d u c e l e a k a g e between t h e door and t h e frame. The r e s u l t s f o r t h e wood door a r e shown i n F i g u r e 3 ; t h o s e f o r t h e s t e e l door a r e i n F i g u r e 4 . Adding w e a t h e r s t r i p a t a l l f o u r edges of t h e door g i v e s s u b s t a n t i a l a c o u s t i c a l improvement. The magnetic w e a t h e r s t r i p p r o v i d e d much b e t t e r h i g h f r e q u e n c y t r a n s m i s s i o n l o s s t h a n
t h e foam s e a l s , b u t gave only s l i g h t l y h i g h e r STC v a l u e s . Wood door S t e e l door Both (no a b s o r p t i o n ) 6 5 mm s e p a r a t i o n 2 2 8 mm s e p a r a t i o n Both ( w i t h a b s o r p t i o n ) 6 5 mm s e p a r a t i o n 2 2 8 mm s e p a r a t i o n
To compare t h e wood door's p o t e n t i a l n o i s e r e d u c t i o n w i t h t h a t of t h e m e t a l d o o r , b o t h were t e s t e d w i t h t h e c r a c k s between door and frame s e a l e d by w e a t h e r s t r i p a t one f a c e , and
a t
t h e o t h e r f a c e w i t h a n impervious t a p e ( t h e heavy s o l i d c u r v e s a t t h e t o p i n F i g u r e s 3 and 4 ) . P r e v i o u s s t u d i e s of sound t r a n s m i s s i o n have shown t h a t f o r small c r a c k s t h i s p r o v i d e s s i m i l a r performance t o c a u l k i n g t h e openings. The m e t a l door had t h e h i g h e r STC b u t w i t h t y p i c a l w e a t h e r s t r i p p i n g , sound l e a k s around t h e door p a n e l would l a r g e l y e l i m i n a t e t h i s d i f f e r e n c e . Without any s e a l s a t t h e p e r i m e t e r (bottom c u r v e s i n F i g u r e s 3 and 4 ) , t h e wood door provided more n o i s e r e d u c t i o n t h a n t h e m e t a l door because t h e c r a c k s between t h e wood door and frame w e r e a b o u t 1 1 3 t h e w i d t h of t h o s e around t h e m e t a l door. The t e s t r e s u l t s f o r"double doors" are f o r one wood and one s t e e l door, b u t u s e of two wood o r two m e t a l d o o r s would n o t g r e a t l y a f f e c t t h e performance. No S e a l W e a t h e r s t r i p F u l l y S e a l e d 22 26
-
30 3 1 17 28-
32 35 29 39-
41 47 3 4 49-
5 0 5 2 4 1 4 3-
45 49 4 3 5 1-
5 3 5 4FREQUENCY, Hz
Fig. 3: Transmission Loss of wood door:
( -
no seals, STC 22;
(
---
)foam weatherstrip, STC 26;
( . -
magnetic weatherstrip, STC 30;
(- )
fully sealed, STC 31.
FREQUENCY, Hz
Fig. 5
:Sound Transmission Loss for
double door with 65
mmairspace:
(---
1
no seals, STC 29;
(
-
)magnetic weatherstrip, STC 41.
FREQUENCY, Hz
Fig. 4: Transmission Loss of metal door:
(- )
no seals, STC 17;
( - - - )
foam weatherstrip, STC 28;
( - - - . )
magnetic weatherstrip, STC 32;
(- )
fully sealed, STC
35.
FREQUENCY, Hz
Fig. 6: Sound Transmission Loss for
double door with 228 mm airspace:
( - - - )
no seals, STC 34;
T e s t r e s u l t s w i t h b o t h d o o r s c l o s e d a r e g i v e n i n F i g u r e 5 ( f o r t h e 65 mm s e p a r a t i o n ) and F i g u r e
6
( f o r t h e228
mm s e p a r a t i o n ) . The dashed c u r v e s ( f o r t h e c a s e w i t h not r e a t m e n t a t t h e p e r i m e t e r of t h e d o o r s ) show t h a t s i m p l e d o u b l e door systems of t h i s t y p e do n o t p r o v i d e h i g h STC. Even w i t h t h e l a r g e r s p a c i n g , t h e STC w a s o n l y
3 4 .
Without s e a l s , most of t h e sound energy goes around t h e d o o r s r a t h e r t h a nthrough them. Reducing t h e sound e n e r g y going around t h e edges of t h e d o o r s , by a d d i n g w e a t h e r s t r i p a t t h e p e r i m e t e r , gave much h i g h e r t r a n s m i s s i o n l o s s a s shown by t h e s o l i d c u r v e s i n F i g u r e s
5
and 6. With t h e l a r g e r s p a c i n g , t h e STC of t h ew e a t h e r s t r i p p e d d o o r s was w e l l above t h e d e s i g n t a r g e t of
45.
Even h i g h e r t r a n s m i s s i o n l o s s was o b t a i n e d by a d d i n g a c o u s t i c a l l y a b s o r b i n g m a t e r i a l t o t h e c a v i t y between t h e two doors. The change i n t r a n s m i s s i o n l o s s from adding
25 mm
of a c o u s t i c a l foam on t h e f a c e of e a c h door i s shown i n F i g u r e 7 f o r b o t h i n t e r d o o r s p a c i n g s . I n b o t h c a s e s , adding a b s o r p t i v e m a t e r i a l i n c r e a s e d t h et r a n s m i s s i o n l o s s n o t i c e a b l y , e s p e c i a l l y n e a r t h e midfrequency d i p (around
1kHz
f o r t h e228
mm s p a c i n g , and s l i g h t l y lower f o r t h e smaller s p a c i n g ) . The t r a n s m i s s i o n l o s s w a s n o t a f f e c t e d s t r o n g l y by t h e amount of a b s o r p t i o n added, a f t e r t h e i n i t i a l25
mm t h i c k n e s s . O v e r a l l , adding a b s o r p t i o n t y p i c a l l y i n c r e a s e d t h e STC by 2 o r 3.T h i s e f f e c t is a p p r e c i a b l y less t h a n t h a t observed when a b s o r p t i o n i s added t o c a v i t y w a l l s . With t h e d o o r s s e a l e d , t h e i n c r e a s e due t o added a b s o r p t i o n was even s m a l l e r and was c o n f i n e d t o a small f r e q u e n c y r e g i o n , a s shown i n F i g u r e 8.
Subsequent measurements of a c o u s t i c i n t e n s i t y showed t h a t t h e change i n r a d i a t e d sound e n e r g y w a s l o c a l i s e d n e a r t h e c r a c k a t t h e door p e r i m e t e r . It seems
r e a s o n a b l e t o a r g u e t h a t t h e a b s o r p t i o n i n t h e c a v i t y i s e f f e c t i v e p r i m a r i l y i n r e d u c i n g t h e e f f e c t of t h e l e a k s around t h e door. FREQUENCY, Hz
-
125 250 500 1 k 2k 4 k FREQUENCY,Hz
Fig.
7
: Sound Transmission Loss f o r Fig. 8 : Sound T r a n s m i s s i o n L o s s f o r d o u b l e door w i t h magnetic w e a t h e r s t r i p double door w i t h228
mm a i r s p a c e and65
mm i n t e r d o o r s p a c e : b o t h doors s e a l e d : (- ) no a b s o r p t i o n , STC41;
(-- -
) no a b s o r p t i o n , STC5 2 ;
(--- ) w i t h a b s o r p t i o n , STC44;
(-) w i t h25
mm a b s o r p t i o n on each228
mm i n t e r d o o r space: door f a c e , STC54.
(-.- ) no a b s o r p t i o n , STC49;
(-) w i t h a b s o r p t i o n , STC52
The n e g l i g i b l e e f f e c t of a b s o r p t i o n a t most f r e q u e n c i e s s u g g e s t s t h a t a i r b o r n e sound t r a n s m i s s i o n through t h e i n t e r - d o o r c a v i t y i s n o t dominant when t h e d o o r s a r e
s e a l e d . The most l i k e l y a l t e r n a t i v e i s v i b r a t i o n t r a n s m i s s i o n through t h e s t e e l
doorframe. I n t h e s e t e s t s , o n l y minor e f f o r t s were made t o c o n t r o l t h i s t r a n s m i s s i o n p a t h , b u t e l i m i n a t i n g s t r u c t u r a l c o u p l i n g would presumably b e worthwhile i f STC v a l u e s a p p r e c i a b l y above 50 a r e d e s i r e d .
The d a t a f o r t h e w e a t h e r s t r i p p e d d o u b l e door systems show some b e n e f i t from t h e a d d i t i o n of a b s o r p t i o n , b u t do n o t p r e s e n t a compelling c a s e f o r i t s use. Without w e a t h e r s t r i p p i n g , however, t h e e f f e c t of added a b s o r p t i o n i s much more obvious. F i g u r e 9 i l l u s t r a t e s t h e i n c r e a s e i n t r a n s m i s s i o n l o s s from a d d i n g a b s o r p t i o n w i t h a
65 mm i n t e r - d o o r space. The c o r r e s p o n d i n g d a t a f o r t h e l a r g e r s p a c i n g are g i v e n i n F i g u r e 10. From a p r a c t i c a l p o i n t of view, n o t o n l y does a d d i n g a c o u s t i c a l
a b s o r p t i o n t o t h e f a c e of one ( o r p r e f e r r a b l y b o t h ) of t h e doors i n c r e a s e t h e n o i s e r e d u c t i o n , b u t a l s o i t limits t h e d e t e r i o r a t i o n i n a c o u s t i c a l p r i v a c y t h a t would o c c u r i f t h e w e a t h e r s t r i p p i n g were damaged o r b a d l y i n s t a l l e d . 0 125 250 500 1k 2k 4k FREQUENCY, Hz 0 t l l l l l l l l l l l l l l l l 125 250 500 1 k 2k 4k FREQUENCY, Hz
Fig. 9 : Sound Transmission Loss f o r Fig. 10: Sound T r a n s m i s s i o n L o s s f o r d o u b l e door w i t h 65 mm a i r s p a c e and no d o u b l e door w i t h 228 mm a i r s p a c e and
w e a t h e r s t r i p p i n g : no w e a t h e r s t r i p p i n g :
(
---
) no a b s o r p t i o n , STC 29; (--- ) no a b s o r p t i o n , STC 34;(- w i t h 25 mm a b s o r p t i o n on e a c h (- ) w i t h 25 mm a b s o r p t i o n on each
door f a c e , STC 41. door f a c e , STC
43.
CONCLUSIONS
1. Double door systems u s i n g c o n v e n t i o n a l door p a n e l s w i t h o u t w e a t h e r s t r i p p i n g o r o t h e r a c o u s t i c a l m o d i f i c a t i o n s w i l l n o t p r o v i d e a n STC much o v e r 30, and t h u s do n o t g i v e e f f e c t i v e speech p r i v a c y .
2. Use of w e a t h e r s t r i p p i n g a t a l l f o u r edges of t h e door g i v e s s u b s t a n t i a l a c o u s t i c a l improvement. These t e s t s s u g g e s t t h a t magnetic w e a t h e r s t r i p i s s l i g h t l y s u p e r i o r t o compressed foam g a s k e t s , w i t h t h e added b e n e f i t s of p e r m i t t i n g much e a s i e r opening and c l o s i n g of t h e door, and a good r e c o r d f o r
l o n g e v i t y i n r e s i d e n t i a l a p p l i c a t i o n s . However, t h e a c o u s t i c a l a d v a n t a g e of t h e magnetic w e a t h e r s t r i p i s s l i g h t , and o t h e r t y p e s of w e a t h e r s t r i p p i n g c o u l d p r o v i d e a d e q u a t e n o i s e r e d u c t i o n performance f o r t y p i c a l a p p l i c a t i o n s . 3 . Adding a c o u s t i c a l a b s o r p t i o n t o t h e f a c e of one ( o r p r e f e r r a b l y b o t h ) of t h e d o o r s i n c r e a s e s t h e n o i s e r e d u c t i o n s t i l l f u r t h e r , and d r a s t i c a l l y l e s s e n s t h e d e t e r i o r a t i o n i n a c o u s t i c a l p r i v a c y t h a t would o c c u r i f t h e w e a t h e r s t r i p p i n g were damaged o r b a d l y i n s t a l l e d .
4 . With w e a t h e r s t r i p p i n g on b o t h d o o r s , and a c o u s t i c a l a b s o r p t i o n between t h e d o o r s , a s p a c e of a p p r o x i m a t e l y 75 t o 100 mm ( 3 t o
4
i n c h e s ) i s r e q u i r e d between t h e d o o r s t o r e l i a b l y a c h i e v e t h e t a r g e t of STC4 5
used h e r e a s t h e i n d i c a t o r of a c c e p t a b l e s p e e c h p r i v a c y .5.
Design of a r e t r o f i t system t o b e added t o e x i s t i n g c o n v e n t i o n a l s i n g l e d o o r s seems t o b e a f e a s i b l e (and a p p a r e n t l y l e s s e x p e n s i v e ) a l t e r n a t i v e t oreplacement w i t h commercial a c o u s t i c a l doors. I n s e n s i t i v i t y t o p e r f e c t i o n of t h e w e a t h e r s t r i p s h o u l d be much improved r e l a t i v e t o t y p i c a l a c o u s t i c a l doors.
ACKNOWLEDGEMENTS :
The f i n a n c i a l s u p p o r t of t h i s s t u d y by t h e S e c u r i t y E n g i n e e r i n g branch of t h e Royal Canadian Mounted P o l i c e , and t h e i r p e r m i s s i o n t o p u b l i s h t h e r e s u l t s , a r e g r a t e f u l l y acknowledged. T h i s p a p e r i s a c o n t r i b u t i o n of t h e I n s t i t u t e f o r Research i n
T h i s p a p e r i s b e i n g d i s t r i b u t e d i n r e p r i n t f o r m by t h e I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n . A l i s t of b u i l d i n g p r a c t i c e and r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e ~ u b l i c a t i b n s S e c t i o n , I n s t i t u t e f o r R e s e a r c h i n C o n s t r u c t i o n , N a t i o n a l Research C o u n c i l o f C a n a d a , O t t a w a , O n t a r i o , K I A
